Image motion and change transducers and systems controlled thereby

ABSTRACT

A system for generating signals indicative of changes in multiple scanned images. The same subject may be scanned at successive intervals or multiple subjects may be scanned simultaneously. In the former situation, signals representative of the scanned image are stored and then compared with signals from a subsequent scanning. Where simultaneous scanning of subjects occurs, signal comparison is immediate. In both cases, output signals are generated in response to changes in the scanned images, the signals being used for positional correction or data readout.

United States Patent [72] Inventor EmilJ. Bolsey 2,420,509 5/1947 Whittaker 244/14.3 160 Concord Ave., White Plains, N.Y. 2,713,134 7/1955 Eckweiler.. 244/14.3 10606 2,826,378 3/1958 Childs 244/14 2 [21] Appl. No. 778,870 7 2,931,910 4/1960 Ostergren et al. 244/14.3 [22] Filed May 27, 1968 3,093,821 6/1963 Alpers et a1 244/14.3 [45] Patented Nov. 2, 1971 2,849,184 8/1958 Fredrick et a1. 343/7 Continuation-impart of application Ser. No. 2,853,700 9/1958 Cherry, Jr 244/14 118,194,.Iune l9, l96l, now abandoned. 2,961,190 11/1960 Miller et a1. 244/14 2,963,543 12/1960 Link et a1 114/20 2,972,276 2/1961 Whitney 250/233 3,080,485 3/1963 Saxton 250/203 3,138,712 6/1964 Aroyan 250/203 IMAGE MOTION AND CHANGE TRANSDUCERS 3,139,246 6/1964 Willits 244/14 AND S YSTEMS C0 NTR 0LLED THEREBY OTHER REFERENCES 24 Claims, 24 Drawing Figs.

Klass, Optical Guidance Deslgned for Missiles, Aviation [52] U.S. Cl 244/3.16, w hp 8, 1958, pp. 67, 69, 71

95/l2.5,89/41 L 511 Int. Cl F41g 9/00, fi' Emile F42!) 15/02 F4lg H/OO Assistant Examiner-Thomas Webb 50 Field at Search 244/3.16;

95/12.5 W" E ABSTRACT: A system for generating signals indicative of [56] References C'ted changes in multiple scanned images. The same subject may be UNITED STATES PATENTS I scanned at successive intervals or multiple subjects may be 2,972,928 2/1961 Maurer 95/l2.5 X scanned simultaneously. In the former situation, signals 2,967,470 l/196l Willits et al... 95/125 representative of the scanned image are stored and then com- 2,922,100 l/1960 Ketchledge... 244/14 UX pared with signals from a subsequent scanning. Where simul- 2,899,882 8/1959 Wilie et al..... 95/l2.5 taneous scanning of subjects occurs, signal comparison is im- 3,065,931 11/ 1962 Dixon et a1. 244/14 mediate. in both cases, output signals are generated in 3,120,360 2/1964 Wylie et a1 244/14 response to changes in the scanned images, the signals being 2,070,178 2/1937 Pettenger et a1 244/ 14.3 used for positional correction or data readout.

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IMAGE MOTION AND CHANGE TRANSDUCERS AND SYSTEMS CONTROLLED THEREBY This application is a continuation-in-part of Application Ser. No. 118,194, filed June 19, 1961 and now abandoned.

The present invention relates to automatic devices for comparing spatial and temporal energy patterns received from one or more energy radiating or reflecting bodies. By detecting and measuring specific changes in said patterns, such as may, for example, result from relative displacements, the devices of the invention produce output signals indicative of the kind and magnitude of said changes. The output signals may control servos, which may then counteract said changes, or they may simply be readout by suitable instruments, depending on in tended application.

While systems of this type have been available heretofore, such previously known devices usually require relatively its method complex, bulky and expensive electronic computers. Moreover, the prior art systems only operate accurately and reliably with certain particular energy patterns and so are limited in application. Generally, the known systems are excessively slow, or they respond only to time-rate of change, thus exhibiting positional drift. Finally, the prior art usually calls for an active system, leading to the generation of undesirable radiative energy.

It is, accordingly, one of the objects of the present invention to provide devices which are inherently free of one or more of the aforesaid difficulties and are therefore suitable for a multiplicity of uses.

It is a further object of the present invention to provide devices which generate specific electrical signals in response to changes occurring in energy patterns, such as optically produced images.

In one particular illustrative embodiment of the invention, a system is disclosed for automatically providing accurate image motion compensation in conjunction with a photographic camera carried by a moving vehicle. In this application, the invention controls the compensatory motions of the camera, or of component parts thereof, to greatly reduce or even eliminate during exposure the relative displacements which tend to occur between the film and the image of a selected part of the subject because of the motions of the vehicle, as is required for the obtention of pictures that are free of motion blur. The device of the invention achieves this automatically by comparing the images produced by the subject in the film plane of the camera at several successive times and by sending appropriate control signals to a conventional servo drive, which may, for example, translate the film along with the image during exposure to essentially eliminate their relative blur-producing motion. In alternate embodiments, the servo drive may either translate internal mirrors or the objective lens, or it may rotate external mirrors, or the whole camera about a pivot in order to effect image motion compensation.

In other applications of the present invention, automatic image comparison may be achieved, which may or may not necessarily be of simultaneously existing images; this can be used to identify those images that are of the same subject, or to check differences between them, such as changes in alignment, in orientation, in size or in other characteristics of the images. In one illustrative application of the invention, such comparison permits accurate aiming, or bore-sighting, of several optical systems to the same target. The invention can also be applied to the accurate navigation of an aircraft, wherein images of the terrain obtained in flight are automatically matched against previously obtained pictures of portions of the desired ground path to provide very accurate fixes of the aircraft position at various times during its flight.

It is an object of the present invention to provide a device which can maintain itself, in a fully automatic manner, aimed at a selected target, irrespective of the relative movement between the device and the target.

An additional object of the present invention is to provide an arrangement where a device can properly orient itself with respect to a selected target, or vice versa, irrespective of inaccuracies of the mounting structure which carries the device.

Still another object of the present invention is to provide an arrangement where a device can be directed toward a target either on the basis of information obtained at the instant of aiming by a human operator or on the basis of previously obtained and recorded information.

Also it is an object of the invention to provide a device which is capable of operating initially with respect to one reference and which is capable of automatically providing a second reference with respect to which it operates when the first reference no longer provides accurate operation.

An additional object of the present invention is to provide a system wherein a considerable amount of mismatching in size, between two patterns will have little influence, the system of the invention operating accurately even with an incoming signal that does not correspond fully with a certain reference signal.

Many other uses of the present invention will present themselves to those versed in the art, who will also recognize readily that the devices of the invention can be adapted to operate, for example, with infrared or ultraviolet energy, with radio waves, or even with sonic waves, without departing from the spirit of the invention.

It is therefore a feature of an embodiment of the invention that scanning means adapted to the type of waves to be used, including at least one aperture, scan at least two related energy patterns and convert spatial changes of energy flux density within said patterns to temporal changes of flux entering said aperture.

It is a further feature of an embodiment of this invention that means are included to detect energy flux, together with amplifying, filtering and switching means to produce at least two signals corresponding to the energy patterns, said means further comparing said signals to produce (a) a first series of pulses having positive polarity whenever the first of said signals changes polarity prior to the second and negative polarity whenever the second of said signals changes polarity prior to the first, and (b) a second series of pulses of fixed polarity whenever said signals differ.

It is still another feature of an embodiment of this invention that generating means produces at least one timing signal varying in relation to a corresponding velocity component of a scanning aperture.

It is yet another feature of an embodiment of this invention that synchronous detection means combine a first series of pulses with a timing signal to produce at least another series of pulses characteristically related to positional differences in image-responsive energy patterns occurring in the direction of a velocity component of motion.

The novel features which are considered characteristic of the invention are set forth in the appended claims. The invention itself, its construction and its method of operation, will be best understood from the following detailed description, given by way of examples only, of specific embodiments in connection with accompanying drawings in which:

FIG. 1 diagrammatically illustrates one possible guidance system according to the present invention;

FIG. 2 diagrammatically illustrates an aiming and tracking arrangement which cooperates with that of FIG. 1;

FIG. 3 is a fragmentary perspective illustration of a package which indicates the scanning and control components of one embodiment of the invention;

FIG. 4 is a simplified functional block diagram showing the electronic circuitry of one form of the invention;

FIG. 5 is a detailed block diagram showing the components ofthe system of the invention located in a missile and in an aircraft from which the missile is launched;

FIG. 6 is a block diagram illustrating the gain control of a photomultiplier using a variable high voltage supply of the system of the invention;

FIG. 7 graphically illustrates two signals typical of the system of the invention;

FIG. 8 shows a front elevational view of a mosaic type of scanner according to the invention;

FIG. 9 is a sectional view of the structure of FIG. 8 taken along the line 9-9 of FIG. 8 in the direction of the arrows;

FIG. 10 shows an antenna scanning arrangement;

FIG. 11 is a simplified view of a scanning assembly in accordance with the invention, showing the possible paths of illustrative optical rays;

FIG. 12 shows a detail of a rotary aperture of the device of FIG. 11 and defines symbols and coordinates used in the description of the system;

FIG. 13 is a functional block diagram of one possible arrangement of the electronic portion of the system;

FIG. 14 illustrates pulse trains which occur at various points of the system;

FIG. 15 shows possible application of the invention to the automatic control of the field angle of an objective lens;

FIG. 16 is an isometric exploded diagrammatic illustration of a structure for automatically controlling a variable focal length lens and a masking disc;

FIG. 17 is an electronic block diagram showing an alternative disposition of part of the system shown in FIG. 13;

FIG. 18 illustrates diagrammatically a scanning technique utilizing a square scan pattern;

FIG. 19 diagrammatically illustrates a ground tracking operation and the switchover from one scanned area to the next scanned area during flight of an aircraft;

FIG. 20 is a simplified block diagram of one system of the invention as applied to ground tracking;

FIG. 21 represents an application of the invention to an automatic V/H sensor of the type used for the control of image motion compensation in aerial cameras;

FIG. 22 illustrates a scanner structure adapted to tracking of the ground;

FIG. 23 illustrates the manner in which a satellite camera may be combined with the system of the invention; and

FIG. 24 illustrates an application of the invention utilizing fiber optics to transmit light from the lens and scanning aperture.

The basic approach of the invention can be explained by way of a description of the application of the system to the automatic guidance of an air-to-ground missile.

The field of view of the apparatus may be in the form of an annulus centered on the selected target. In FIG. I, this annulus is continuously scanned through the equivalent of a rotating radial aperture, including a rapidly rotating prism 10, a fixed aperture 12 and an objective lens 13. This arrangement is far simpler than all-electronic scanning, does not involve any linearity or retrace problems, and allows wide freedom in the choice of spectral sensitivity of the photodetector 16. Moreover, it is active I00 percent of the time, thus delivering information at a maximum rate. Since the aperture 12 functions as an optical field stop, no other such field stop is needed. This eliminates aperture modulation, i.e., the generation of spurious signals due to the scanning of a separate field stop by aperture 12. In effect, this high-speed rotary scanning system dissects the image of the target-surrounding terrain. The image is converted to an electrical signal which represents the brightness of the terrain as a function of time over each scan. Since the image is scanned repetitively, the electrical voltage which represents any scan can be compared to that representing any other scan.

Since the target viewed repeatedly from the same aspect generates an identical electrical signal on each scan, comparison of scans for a missile which heads directly toward the target will produce no substantial error signal. However, if the target aspect changes, the images will no longer exactly coincide, and comparison of corresponding scans will produce an error signal.

At selected times during travel of a vehicle carrying the apparatus of the invention, the video scanner output, appearing in the output of amplifier 16A, derived from photosensitive detector I6, is stored in a magnetic recording memory unit 17, allowing subsequent scans to be compared with the stored one. The recorded scan may also be periodically erased and a new scan immediately recorded.

To facilitate further processing, the two video signals resulting from a first scan and a subsequent scan, are converted to binary signals. This conversion is obtained by triggering two bistable multivibrators or flip-flops l4 and 15 from the differentiated video signals. This is accomplished by applying the first video signal from the storage unit 17 to a differentiating circuit 17A and the second video signal from amplifier 16A to a differentiating circuit 168. The outputs of the flip-flops consist of two series of constant amplitude pulses of variable width and time position.

Let these two series of pulses be designated by V,(l) and V (t), where V, is the binary transform of the recorded scan and V, is the binary transform of any subsequent scan.

Binary coding of V, and V allows them to have only two discrete values. Circuit design is such as to cause these values to be equal in amplitude but opposed in sign. Thus V,(t)":a and V (t)=:ta.

The degree of correlation between V, and V 2 is next obtained by a multiplication process in a balanced modulator lthe output of which is V, =i'ka where k is a constant. If there was no change in the field of view between the two scans, then V,==V and the output of modulator v,,=ka, i.e., pure DC. Actually, the ever present system noise causes some random pulses of reverse polarity. V, does not, however, show any definite periodicity. In modulators M and M intermixing of signal V,,, which is carried out with in-phase" and in-quadrature" signals at scanning frequency, will thus produce no net output. These in-phase and in-quadrature signals applied to modulators M and M are derived from AC power sources S, and S which are supplied to the windings W, and W of a synchronous motor S which serves to rotate prism 10 at the desired scanning rate. The intermodulation ofsignals S and S with V in modulators M and M involves a process commonly known as synchronous detection.

A small positional change within the field of view occurring between the scans will generally cause V, to be different from V V will then comprise substantial negative error" signals. The character of these error signals depends directly on the kind of motion causing the change within the field of view. If the motion is a simple translation on the optical axis, there again will not be periodicity in V,, and no net output will appear at M, and M,.

A lateral displacement, however, causes the equivalent of a modulation of the scanning velocity. When image displacement and scanning are in the same direction, the relative scanning velocity is lowered by an amount depending on the rate of lateral image displacement. Conversely, when image displacement and momentary scanning direction are opposed, the relative scanning velocity is increased. It is thus clear that the relative scanning velocity undergoes a sinusoidal phase modulation. This in turn causes alternate spreading and bunching of signal V,. This effect is a periodic one and occurs at scanning frequency. Its phase relative to the scanning process is entirely determined by the direction of image displacement. Therefore, the output of M and M now yields DC motion signals of a magnitude and sign directly related to the components of the above displacement in two orthogonal directions referred to as vertical" and horizontal in FIG. 1. These signals may be used, for example, to steer the vehicle carrying a device in accordance with the invention, back to its target.

The ultimate accuracy of the sensor is essentially limited only by image quality (optical resolution) and system noise. With good visibility, an accuracy of a small fraction of a degree is entirely practical. To exploit such capability, a correspondingly accurate and stable aiming device must be available. Moreover, means to align such aiming device and to maintain it in equally accurate alignment with the missile optical guidance system are also required. However, boresighting cannot be relied upon to line up the missile guidance and the aircraft aiming systems, since mechanical tolerance buildup between major assemblies of the missile, of its launcher, of the aircraft, as well as their static and dynamic deflections, contribute alignment errors far too great to be tolerated. 

1. In a guidance system, in combination, scanning means for scanning a selected area, said scanning means operating cyclically to provide at least one scan having a given video pattern; photosensitive means cooperating with said scanning means for changing each said video pattern into electrical signals which are respectively the analogs of said video patterns; quantizing means cooperating with said photosensitive means for converting the electrical signals produced thereby into binary signals; delay means cooperating with said quantizing means for providing a delayed binary signal; a source of a reference binary signal; delay means for delaying the reference binary signal; a pair of cross-multiplying means cooperating with said source, said quantizing means, and both of said delay means for cross-multiplying a delayed binary signal from said quantizing means with an undelayed binary signal from said source and for cross-multiplying an undelayed binary signal from said quantizing means with a delayed signal from said source; means cooperating with said pair of cross-multiplying means for determining the difference between the pair of crossmultiplications; a second reference source, said latter reference being capable of discriminating, when multiplied with said crossmultiplications, between errors in yaw, pitch, or roll; and means for correcting the position of said scanning means according to the errors determined.
 2. A guidance system in accordance with claim 1 including means for differentiating and filtering said electrical signals generated by said photosensitive means to eliminate the DC component and to attenuate the lower frequency components thereof.
 3. In a guidance system, in combination, a carrier; a pair of recording tracks carried by said carrier, one of said recording tracks carrying a reference signal; means cooperating with the other of said recording tracks for recording onto the latter an incoming signal and for simultaneously erasing any previously recorded signal from said other track; correlating means cooperating with said incoming signal and said reference signal for correlating said signals to determine when a new reference signal is required; and gating means activated by said correlating means and cooperating with said tracks for retaining an incoming signal on said other track and for starting said erasing and recording on said one track when said correlating means determines the need for a new reference signal, so that said tracks operate alternately to carry a reference signal and to receive incoming signals.
 4. A guidance system in accordance with claim 3 including additional ones of said recording tracks for receiving thereon correspondingly additional ones of said reference signals.
 5. Apparatus for detecting changes occuring in an image formed by a pattern of radiant energy in which image components are displayed in contrasting energy levels, said apparatus comprising: A. means including a transducer responsive to said radiant energy to scan a predetermined section of said image during a first period to produce a first electrical signal which is a substantially uninterrupted voltage analog representative of said scanned section in said period aNd to scan said section during a later period to produce a second electrical signal which is a substantially uninterrupted voltage analog representative of said scanned section in the later period, B. means recording the first signal during the first period and to play back said recording during the later period to provide a reference signal, and C. means to measure the degree of correlation between the reference signal and the second signal to produce an error signal which is a function of the changes occurring in said section of said image between said periods and which is constituted by error components in three coordinates.
 6. Apparatus, as set forth in claim 5, wherein said transducer means includes means responsive to said radiant energy in the form of light.
 7. Apparatus, as set forth in claim 5, wherein said transducer means includes means responsive to said radiant energy in nonvisible form.
 8. Apparatus, as set forth in claim 5, wherein said correlation measuring means includes means responsive to analog and digital signals.
 9. Apparatus, as set forth in claim 5, including means for automatically controlling the field angle at which said scanning means views said image to minimize said error signal.
 10. Apparatus, as set forth in claim 5, wherein said transducer includes: A. an objective for directing an image of a subject onto the focal plane of the objective, B. a rotary disc disposed at said focal plane and having an axis of rotation which at least intersects said image, said disc having an aperture therein spaced from said axis of rotation whereby in the course of rotation an annular section of said image is scanned by said aperture, and C. a radiant-energy sensitive device positioned at the side of the disc opposed to said objective to intercept radiant energy from the scanned annular section and to convert the energy into an electrical signal which is an uninterrupted voltage analog thereof.
 11. Apparatus, as set forth in claim 10, wherein said aperture is formed by an elongated radial slot in said disc.
 12. Apparatus, as set forth in claim 11, wherein said radial slot has a wedge-shaped configuration.
 13. Apparatus, as set forth in claim 11, further including means to adjust the width of said radial slot.
 14. Apparatus, as set forth in claim 11, further including a masking disc coaxial with said scanning disc and rotatable therewith, said masking disc being formed with a helical slot part of which extends across said radial slot so that by relative angular displacement of said masking and scanning discs, a selected portion of said radial slot will be exposed to pass radiant energy from said objective.
 15. Apparatus, as set forth in claim 10, wherein said objective is adjustable and further including means automatically adjusting said objective to maintain the objects represented in the scanned image of substantially the same magnitude during relatively large changes in distance between the subject and said objective.
 16. Apparatus, as set forth in claim 14, further including means to adjust the angular relationship between the masking and scanning discs during a change in the distance between a subject and said objective for retaining in the scanned annular section the same objects during a relatively large change in the distance between the subject and the objective.
 17. Apparatus for detecting changes occurring in an image formed by a pattern of radiant energy in which image components are displayed in contrasting energy levels, said apparatus comprising: A. means including a transducer responsive to said energy to scan a predetermined section of said image during a first period to produce a first electrical signal which is a substantially uninterrupted voltage analog of said scanned section in said period and to scan said section during a later period to produce a second signal which is a substantially uninterrupted voltage analog of said section in the later period, B. means to quantize said first and second signals to produce first and second trains of pulses of varying width and spacing which is a function of the analog values of said signals, and C. means recording the first train of pulses during said first period and to play back the recording during said second period to provide a reference train of pulses, and D. means to measure the degree of correlation between said reference train and said second train to produce a train of error pulses which represents the changes occurring in said section of said image between said periods and which is constituted by error components in three coordinates.
 18. In a camera system subject to displacement relative to an area being viewed, A. optical means to produce an image of said area, which image changes with said displacement, B. means including a photocell to scan a section of said image during a first period to produce a first video signal representative of said section and to scan said section of said image during at least one later period to produce a second video signal representative of said section at the later period, C. means to quantize said first and second video signals to produce first and second trains of pulses of varying width and spacing which are a function of said signals, D. means recording the first train during said first period and to play back the recording during said second period to provide a reference train of pulses, and E. means to compare said reference train and said second train to produce a train of error pulses which represent the extent and direction of the displacement occurring between the first and second periods in three coordinates.
 19. In a camera system as set forth in claim 18, further including means responsive to said error train to shift the position of said image to effect image motion compensation.
 20. In a camera system, an image motion compensation apparatus comprising: A. an optical device producing an image of an area, which image changes with motion of said camera system, B. a scanner including a photocell to cyclically scan an annular section of said image to produce during one cycle a first video signal which is an analog of said section as it appears in said cycle, and during a subsequent cycle a second video signal which is an analog of said section as it appears in said subsequent cycle, C. means to quantize said first and second signals to produce first and second trains of pulses of varying width and spacing which are a function of said signals, D. means operatively coupled to said scanner and including a circular magnetic recording track to record said first train concurrently with the scanning action during said first cycle and to play back the recording during said subsequent cycle to produce a reference train, E. a circuit for measuring the degree of correlation between said reference train and said second train to produce a train of error pulses which represent the extent and direction of motion occurring between the two cycles, and F. a servomechanism responsive to said error train and coupled to the camera system to effect image motion compensation.
 21. A guidance system for guiding a vehicle toward a selected target, said system comprising: A. means cyclically scanning an area enclosing said target to produce during a selected cycle a first electrical signal which is a substantially uninterrupted analog voltage representative of the image of said target at that time, and to produce during at least one subsequent cycle a second electrical signal which is a substantially uninterrupted analog voltage representative of the image of said target at a later time, B. means recording said first signal during said first cycle and for reproducing said recording during said subsequent cycle to provide a reference signal, C. means to measure the degree of correlation between the reference signal and the Second electrical signal to produce a control signal having components in pitch, yaw and roll which depend on the shift in position of said target relative to said vehicle in the interval between the first cycle and the subsequent cycle, and D. control means disposed in said vehicle and responsive to the components of said control signal to maintain said vehicle oriented towards said target.
 22. A guidance system, as set forth in claim 21, further including means to determine the degree of correlation between said reference signal and said second signal to produce an electrical signal dependent thereon, and means actuated by said electrical signal, when a given reference signal no longer affords a given degree of correlation, to create a new reference signal.
 23. A guidance system, as set forth in claim 21, further including a gimbal structure for supporting said scanning means and control means responsive to signals derived from said scanning means to maintain said gimbal structure oriented towards said target, and means coacting with said control means to render same temporarily inoperative when there is a loss of signals.
 24. A guidance system, as set forth in claim 23, wherein said gimbal structure also carries gyro means, and further including means to render said gyro means operative when said control means is rendered inoperative, said gyro when operative maintaining said scanning means at the orientation it had just prior to said loss of signals. 